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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

262

WHITE METAL

all the antimony and tin (see i, 2} and the residue insoluble in sodium
sulphide the copper and lead and also any zinc and iron present (see 3, 4).

1.  DETERMINATION OF THE ANTIMONY.    The filtrate is treated with
7-8 grams of pure potassium cyanide (precipitated by alcohol) and elec-
trolysed at the ordinary temperature to determine the antimony :  Classen
capsule cathode ] disc or spiral anode ; ND100 = 0-15-0-17 amp. ; voltage
= i-i-2 ; and duration = 15-17 hours.

When the whole of the antimony is deposited, the electrolyte is poured
into a f-litre flask and the capsule and disc (or spiral) washed with a little
water which is also poured into the flask. The capsule is then thoroughly
washed with water, alcohol and ether, dried at 70 and weighed.

2.  DETERMINATION OF THE TIN.    The alkaline liquid freed from anti-
mony is acidified faintly with dilute sulphuric acid (i vol. acid, 2 vols. water),
the flask being kept under a hood, covered with a funnel and shaken.    The
liquid is then boiled for some time to expel the bulk of the hydrogen sulphide
and cyanogen compounds, left on a boiling water-bath for about 15 minutes
and filtered   through a filter-paper moistened with ammonium sulphate
solution, the precipitate being washed with a little hot water saturated
with hydrogen sulphide.

The filter and precipitate are then heated to boiling in a small covered
beaker with 20 c.c. of cone, hydrochloric acid and 15-20 c.c. of 10% ammo-
nium chloride solution, a few crystals of potassium chlorate being sub-
sequently added to complete the action. The liquid is then diluted with
15-20 c.c. of boiling water, shaken and filtered into a -|-litre flask, washing
with hot water acidified with hydrochloric acid. The filtrate is rendered
slightly alkaline with ammonia, treated with 5 grams of oxalic acid and
heated a little, 5 grams of ammonium oxalate being added to the clear
solution, which is then made up to 150-200 c.c. and subjected to a moderate
current of hydrogen sulphide while gently boiling. Under these conditions
the traces of copper dissolved in the sodium sulphide and also any arsenic
present are precipitated. After about an hour the liquid is allowed to cool
somewhat in the stream of hydrogen sulphide and is then filtered into a
-|-litre beaker and the filter washed with a hot 1% oxalic acid solution
saturated with hydrogen sulphide. The filtrate is boiled with 25 c.c. of
cone, hydrochloric acid and 12-14 grams of ammonium oxalate for about
15 minutes to expel the hydrogen sulphide, allowed to cool a little, treated
with 3-4 drops of 30% hydrogen peroxide, boiled again, cooled to about
50 and, without removal of any suspended sulphur, electrolysed to deter-
mine the tin (see Electrolytic Determination of Tin in Ordinary Bronzes).

3.  DETERMINATION OF THE COPPER AND LEAD.   The filter and hydrogen
sulphide precipitate (see 2) are incinerated in a small dish and then ignited,
the residue being dissolved in 2-3 c.c. of nitric acid.

The sulphides remaining undissolved in the sodium sulphide (see A]
are dissolved in 10-15 c.c. of boiling nitric acid (D 1-2), filtered by decan-
tation, the residue being treated again twice with nitric acid and the united
nitric acid solutions (including that from the hydrogen sulphide precipitate)
used for determining the lead and copper as well as any zinc and iron present.

If the copper preponderates'over the lead, as is usual with alloys of thisof ammonium oxalate and acidified with oxalic acid, at 70-80. The coppered cathode